A wide variety of diffuser types for centrifugal pump and compressor stages have been employed over the past several decades. In some cases, a good impeller has been designed first, and then a good diffuser is designed next, or the two elements are designed concurrently. Regardless, essentially all past work has been based on the quasi-steady/axisymmetric assumption of diffuser inlet flow which has typically been treated simply as a one-dimensional (1D) velocity triangle model for preliminary design. Much of these assumptions carry over even with computational fluid dynamic (CFD) models used today. It has typically been assumed, at some level, that the flow leaving an impeller, regardless of the number of blades, and then entering the diffuser, again regardless of the number of vanes, is essentially periodic and axisymmetric, and completely and uniformly fills each diffuser passage.